Origin and evolution of social behavior: case study on genus Ceratina (Hymenoptera: Apidae)

Small carpenter bees of genus Ceratina are very suitable models for research of the origin and evolution of eusociality. Most of Ceratina species are solitary (Michener, 2007) and some are socially polymorphic (Sakagami & Maeta, 1989; Rehan et al., 2009). Socially polymorphic species belong to different unrelated clades of genus Ceratina (Rehan et al., 2009; Rehan et al., 2010). Social behavior therefore either must have arisen several times independently, or it represents original state for the whole genus and solitarity arised secondarily.

There is similar pattern of social traits in family Halictidae (Danforth, 2002). Social behavior of bees from the genus Ceratina is less known than in family Halictidae, although observation of Ceratina is easier than bees of family Halictidae because Ceratina nests in twigs and Halictidae nests in ground. The sister taxon of Ceratina is tribe Allodapini (Cardinal et al., 2010). All Allodapini are considered as eusocial (Tierney et al., 2008). Ceratina is a mass provisioner on the contrary from Allodapini, which are progressive provisioners (Michener, 2007).

Ceratina chalybea

Females of small carpenter bees of genus Ceratina nests in twigs with soft pith (Michener, 2007; Sakagami & Laroca, 1971). Bees firstly excavate burrow. Afterwards they provision cell by pollen and nectar. When they complete the provisioning of the cell, they oviposit and close the cell by septum. (Maeta et al., 1997). Bees usually provision about eight cells per life. After provisioning and oviposition females stay upstairs in burrow and guard offsprings against predators and parasites (Sakagami & Maeta, 1977; Rehan & Richards, 2010). This behavior is quite unique, because in most solitary species female provisions most of her life and the nest is unprotected from attack of predators and parasites most of the time. Parazitation can markedly reduce number of bee´s offspring (Vickruck et al., 2010). The failure of the whole nest because of usurpation by other Hymenoptera or Salticidae spiders, or predation of brood by Dermaptera (unpublished results) is very common.

Marked female defending her nest by own abdomen and Salticidae spider usurping nest of Ceratina

If female is in the burrow after the completing of the cells and she blocks the entrance by her abdomen, predators and parasites can´t entry nest. Similarly social nesting significantly decreases probability of parazitation and total failure of nest, because nest is always protected by at least one female (Rehan et al., 2011). After new adults are hatched, mother feed them by pollen and nectar (Sakagami & Maeta, 1977). In some species young adults are fed not by mother, but by sisters (Sakagami et al., 1989). Females of some species are able to reuse nest. This ability is probably very important for social nesting, because most of nests inhabited simultaneously by more than one female are nests reused (Sakagami & Maeta, 1984, 1989; Rehan et al., 2010). Temperate species usually leave the nest and make new burrows for overwintering. (Sakagami & Laroca, 1971), but sometimes overwinter in natal nests (Rehan & Richards, 2010).

Nest of Ceratina cucurbitina - on the left are fresh new adults, in the middle pupae and on the right larva and old adult female

Nest od C. chalybea with provisioned and epmty cells

In some species more individuals are in some nests (Sakagami & Maeta, 1977; Rehan et al., 2010). Wilson (1971) stated three features of eusociality: reproductive division of labor, cooperative brood care and generation overlap. Published studies (Sakagami & Maeta, 1977, 1989; Rehan et al., 2010, 2011) indicate that eusociality occurs in some species of genus Ceratina. Females of social nests have usually different size of ovary (Rehan et al., 2010; Maeta & Sakagami, 1995). There are probably differences in reproductive success between females in some nest. There is probably overlap of generation, because females in some nest have distinctive differences in wing and mandible wear (Sakagami & Maeta, 1989). For quantification of proportion different types of social organization (eusocial, semisocial and quasisocial) are essential high resolution molecular marker. Azuma et. al. (2005) developed microsatellites for species Ceratina flavipes, but they are not sufficiently variable for assess relationship between individuals.

Researches of social and nesting habits of Ceratina used mainly two methods: dissection of nests (Rehan et al., 2009, 2010, 2011; Sakagami & Maeta, 1989) or observation in laboratory conditions (Sakagami & Maeta, 1989; Maeta & Sakagami, 1995). There are not any studies of behavior in nature conditions. Most of researches were done in Japan (Sakagami & Maeta, 1977, 1987, 1989; Maeta & Sakagami, 1995), North America (Rehan & Richards, 2010) and Australia (Rehan et al., 2010, 2011). Nesting biology of European species is almost unknown. There is four species in Czech republic: Ceratina chalybea, C. nigrolabiata, C. cyanea and C. cucurbitina (Straka et al., 2007). Our aim therefore is to learn more about biology and especially social state of these species using behavioral observation and field experiments as well as molecular genetic methods.

Chenoweth L.B., Tierney S.M., Smith J.A., Cooper S.J.B. & Schwarz M.P.2007: Social complexity in bees is not sufficient to explain lack of reversions to solitary living over long time scales. BMC Evolutionary Biology, 7:246